This invention relates to methods and systems for identifying fluids and determining fluid flow rates and, more particularly, to methods and systems for determining gas flow rates using a hot wire anemometer.
Instruments which rely upon controlled fluid flow are commonly employed in a wide variety of applications, such as sample purification, chemical analysis, clinical assay, and industrial processing. Many instruments, such as high pressure liquid chromatographs (HPLC), gas chromatographs (GC), clinical analyzers, and flow-injection analyzers, require precisely-controlled flow.
It is known in the art to determine gas flow rates by determining the flow rate with a hot wire anemometer. In a hot wire anemometer, the gas typically is passed over a single heated wire, reducing the temperature of the wire. The change in resistance of the heated wire is determined and correlated with the flow rate of the gas. A more advanced technique employs two temperature sensing elements located a fixed and equal distance from a heat source. The gas is passed through the system, reducing the temperature of the upstream sensor and increasing the temperature of the downstream sensor. The temperature difference is then recorded as an output signal.
One major drawback of hot wire anemometers is the nonlinear and fluid-dependent manner in which they respond to fluid flow. Thus, the output signal is rarely useful by itself and must typically be augmented by other data. For applications wherein multiple gases are employed, both gas type information and the calibration curves corresponding to each of the different gases are necessary to determine the flow rate. A computer can be used to linearize or calculate flow rate from calibration curves. However, gas type information must first be fed into the computer in order to do so. Data processing in this manner requires initial identification of the gas and the performance of time-consuming data input steps.
It would thus be of great advantage in determining fluid flow to provide a flow system which is capable of automatically identifying the type of fluid passing through the system. It would also be of great advantage to provide a system which is capable of determining the flow rates of different fluids from a single, linearized response curve.